The milbemycins are a series of thirteen macrolide antibiotics isolated from the fermentation broth of a strain of Streptomyces identified as the B-41-146 strain. Nine of the milbemycin compounds and their preparation are disclosed in U.S. Pat. No. 3,950,360 issued Apr. 13, 1976 to Aoki et al. A complete disclosure of all thirteen of the milbemycin antibiotics is found in the Journal of Antibiotics 29 (6) June 1976 pages 76-35 to 76-42 and pages 76-14 to 76-16. The compounds are disclosed as having insecticidal and acaracidal activity.